It was an amazing turnaround -- and I'm as pleasantly shocked by it as you.

Let's go back to 2012 for a moment. At the time of his dismissal from the Tigers, LSU was ranked No. 1 in the USA Today Coaches Poll and Mathieu was coming off a season in which he had been a Heisman Trophy finalist. But LSU had had enough -- and that says something. Consider that this summer, Miles opted to let his players vote on whether or not to discipline troubled running back Jeremy Hill. That tells you how bad things were for Mathieu. Miles clearly didn't want to lose him, but he had to.

Mathieu's elite playmaking skills didn't matter; he had run afoul of team rules. Drug abuse was at the root, as Eli Saslow brilliantly documented in ESPN The Magazine leading up to April's draft. Mathieu's priorities were out of whack, and he was branded as a bad and irresponsible seed. When he lost his chance to play football in the fall of 2012 -- a chance he'll never get back -- LSU's title hopes died. And his draft stock seemed to plummet simultaneously. How could any NFL team bank on Mathieu?

But then the Arizona Cardinals selected him in the third round of the draft. And my jaw dropped.

Steve Keim, who was promoted to the general manager position in January, has a tremendous track record when it comes to scouting and picking players during his long tenure with the Cardinals. (Don't forget: Keim was the one who wanted to pick Adrian Peterson instead of Levi Brown in 2007.) Keim's a true football guy; that he would want to draft Mathieu didn't make any sense to me.

Then there was Bruce Arians, going through his first draft as a head coach. This was the most involved Arians had ever been in a war room; maybe Keim, who wants to be on the same page as his head coach when it comes to the draft, was following Arians' lead on this one. But I knew Arians to be a no-nonsense type who preaches discipline and work, so the pick didn't make any sense from that angle, either.

Then, after I picked my jaw up off the floor, it hit me:

These bright and well-respected guys didn't just take a late-round flier on Mathieu; they spent a valued pick on him -- in their first-ever draft in their respective positions -- because they believed. They knew the risk, but they were convinced this guy would be worth it. Very convinced.

And now, Tyrann Mathieu has a chance to be one of the true immediate-impact rookies in the NFL this season -- potentially the steal of the draft.

I can't believe I'm writing that.

"Just like I said when we drafted him, it was a risk," said a candid Keim on "Schein On Sports," my SiriusXM Radio show. "Now, every player you draft is a risk, whether it's for skill, injury, or off-field concerns. We had some off-the-field concerns about him. He's answered the bell. He's been a model citizen so far. Again, he has to stay focused and keep that trend going. The on-field stuff is as good as you can imagine. He is a ball hawk, playmaker; he's tough as nails. The other night, Bruce told me that he got his first live game action late first quarter, second quarter, played in the third, and they tried to take him out of the game and he didn't even want to come out. He's just a competitor. The guy said he sat out of football for a year, he waited long enough, he wants to be out on the field. He just has a unique, real uncanny way about playing the nickel and that slot, blitzing off the hash, doing different things in coverage. I think the NFL is going to see that Tyrann is the real deal."

I've talked to players and staff who have been around Mathieu since he was drafted, and there's been no attitude. There's been no sense of immaturity. He hasn't been lazy or self-centered or acted like he's accomplished anything. He's been the total opposite of a hooligan: being attentive in practice and meetings, working hard on the field, handling media and community relations requests. Mathieu also has been fantastic when it comes to working with kids and youth groups.

Consider where he was one year ago. This is a big deal.

This year, Keim expects Mathieu to play and contribute right away for the Cardinals.

"No doubt," Keim said. "He will play in the return game for us; we'll do some dual return stuff with him and Patrick (Peterson). He will play the nickel for us; he'll play some corner, some safety. We'll try to get him involved as much as possible. He's just one of those guys; the way he played the other night, we want to make sure he's on the field for us. He plays bigger than his measurables. You'd think he'd shy away from contact, (but) I mean, he's trying to stick his face in there, every snap."

There was another factor at work before the draft: Keim and Arians felt like they had great inside information from Peterson, Mathieu's old LSU teammate, who has been incredibly impressive himself as a cornerback and person in Arizona. Peterson's opinion carried weight.

As Keim explained, "the day that Patrick walked through the door here in Arizona, he was as mature as I've seen, from a young guy's perspective. He's driven; he's a real pro's pro. When Patrick vouched for him, I knew that there was probably something there to the kid. (Mathieu) learned his lessons the hard way, and again, he has a long hill to climb. I think he's on the road to recovery, and I think he's going to do a good job for us this year. Patrick has taken him under his wing; so have the rest of our players. Larry Fitzgerald and all those guys; if you saw his punt return the other night -- I think he had a 20-something-yard punt return -- and he came off the field and Fitz was the first one smacking him on the helmet. These guys have fallen in love with the kid. We're hoping for success from him here in the future."

I'm not naïve, and I don't think the Cardinals are, either. Mathieu is not out of the woods yet. Recovering addicts are always recovering.

But I thought it was a great sign of maturity -- and self-awareness -- this week when Mathieu said this to the media in Arizona: "Everywhere I go, I hear encouraging words. 'Good luck,' 'Hope you stay clean,' 'Hope you come here and make plays like you did at LSU.' "

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He doesn't shy away from his problems.

And here's the educated guess for this season: Mathieu makes plays like he did at LSU. He has an unbelievable gift. I think he will be in the mix for Defensive Rookie of the Year, validating the choice made by Keim and Arians.

A year ago, I thought Mathieu was irresponsible and selfish, someone who couldn't possibly fit in the NFL. Now I'm rooting hard for him.

Under Arians and Keim, with the leadership of Peterson and Fitzgerald, and with his dedication, Mathieu has a chance for greatness.